Sound producing device



Nov. 14, 1933.- J. s. HIGH 1,935,185

' SOUND PRODUCING DEVICE Filed June lO. 1931 2 Sheets-Sheet l Nl/ENTOR.Jurgen 5.1'Ilgh, BY Qi ATTORNEY Nov. 14, 1933. J. s. HIGH 1,935,185

SOUND PRODUCING DEVICE Filed June 10', 1931 2 sheets-sheet 2 .I NV ENTOR.

d uT' en 5. Hgh,

ATTORNEY. C

Patented Nov. 14, 1933- l UNITED sTATl-:s PATENroFl-ICE I SOUNDPRODUCING DEVICE Jurjen S. High, Oaklyn Manor, N. J., assignor to RadioCorporation of America, a corporation of Delaware Application June 10,1931. Serial No. 543,341

a a 25 claims. (c1. 214-6) t :My inventionjrelates .to sound-producingderated fromweach other by linear valve seat elevices `and,moreparticularly, to loudspeakers of ments which cooperate with thevalve-head to the air-*flow type. a i throttle'V the elementary aircurrents in yparallel There have been many attempts to devise a relationduring their passagel from sources to loudspeaker whereby, through thecontrol or sinks. vThe latter communicate by a'hornfwith 60,

modulation of an air-current, tremendous sound.-I the atmosphere. y loutput could be obtainedfrom a phonograph.. Thus `the valve seat is thelocus ofa source, from a radio-receiver or from any appropriate a sink,and a throttle area, of which the ele-v source. For the purpose ofcontrolling the airments are enmeshed according to a sequence current,slidingvalves, poppet valves and valves indicated by the followingnotation: Sink,

of many other types have been tried. v throttle, source, throttle, sink,throttle, source,L

Substantially al1 Valves of the poppet type. throttle, sink so thateachsource slit is lohave the drawback of high initial leakage,causcated between two throttle surfaces as well as ing hiss; they have arelatively high air conbetween two sink slits. Y

sumption and they are limited as to their fre- The advantage .of such avalve seatarrangequency-range and load-carrying capacity. Slidment isthat the ratio 70 ing` valves vare prone to overshoot at low frequenciesin the event that .they are adjusted 1mm-Mm' for optimum high-frequencyresponse, even total smk area' though cushioning devices are provided,although can be so chosen thatfthe resultant of the aerothey are fairlysatisfactory insofar as their static and aerodynamic forces which, afteradrather limited frequency-range is concerned. mission 0f air-fiOW, areactingl 0n both SidesOf They also are prone to stick during operationthe plate-Shape Valve head, Will be Substantially and precaution must betaken to prevent foreign Zero fel a Certain Constant input ail Pressureat substances from getting between the valve and which the valve isnormally operated. The mass seat. of the valve head being extremelysmall, a` rela- It is, accordingly, an object of my invention tivelySmall amount 0f stiffness is ,necessary t0 to provide valve mechanismfor air-flow loudobtain a resonant frequency sufiiciently high tospeakers that shall have the advantages of both cover the requiredfrequency range. Therefore,

poppet` and slide valves and the disadvantages the efnciency of thevalve is comparatively high.

of neither. The novel features that I consider character- Another objectof my invention is to provide istic of my invention are set forth withpartienan improved air-flow loudspeaker that shall have lalily in theappended Claims. The inventionv frequency and fidelity characteristicscomparable itself, however, both as t0 its vOrganization and with thoseof the best electrical loudspeakers. its method of operation, tOgethel'With additional A further, and more specific object of my inobjects andadvantages thereof, will best be vention, is to provide a device of thetype deunderstod from the following description of a scribed that shallbe stable in operation and specific embodiment when read in connectionfree from non-linear distortion. with the accompanying drawings, inwhich:

My invention is characterized, broadly, by the Fig. 1 is a sideelevational view of my improvision of) a valve-chamber which, at oneside proved valve-mechanism for air-now loudof a movable valve-head,communicates with the speakers illustrating the connection thereto ofatmosphere through a channel, the air-iiow reactuating means, s istanceof which may be controlled to bias the Fig. 2 is a sectional view of thevalve-mechavalve-head. nismA `taken along a line corresponding to the Itis, furthermore, characterized by the fact line II-II in Fig. 1, lookingin the directionof the that said valve-chamber accommodates a valvearrows, and seat wherein a system of linear, that is, slit- Fig.3 is anexploded view, in perspective, showshaped air-flow sources and a systemof linear ing the laminated construction of the valve-seat.

air-flow sinks are located. The air currents l Referring to Figs. 1 and2 of the drawings, an 105 yielded by the sources are operating inparallel air-flow loudspeaker constructed according to my `relation, asalso are the air currents absorbed invention comprisesavalve-chestlwhich merges by the sinks. The sink system cooperates ininto the small end of an exponential horn 3 in series relation with thesource lsystem, the which chest are included an improved valve-seatsources being enmeshed with the sinks and sepa.` 5 and. a Valve-head '7.The valve-head is conno nected to the vibratory element of a drivingdevice 9 by means of a light, rigid rod 11 which extends through astuffing-box 13 or packing gland provided with means, such as a washer15 of soft rubber, or the like, for preventing air leakage.

The driving device, the valve-chest and the horn may be suitablysupported from a rigid metal base-plate 17 and means are provided topermit moving the driving device, relative to the valve-chest, toprovide for adjusting the armature clearance in the driving device.

As shown in Fig. 1 of the drawings, the driving device may be carried bya plate 19 having a flexible portion 21, the end of the plate nearestthe flexible portion being permanently affixed to the base-board and theother en'd thereof being movable with respect thereto. A resilientwasher 23 or the like may be disposed between the movable end of theplate and the metal base-plate and an adjusting screw 25 may be providedfor urging the plate against the said washer.

The angularity of the plate 19 with respect to the base-plate,therefore, is under the control of the adjusting screw and, since therelatively flexible armature is connected by the rod 11 to therelatively stii valve-head mounted upon the plate 17, the armatureclearance may be adjusted by tightening or loosening the said screws.

It is not to be inferred, however, that I am limited to the armatureclearance adjusting means illustrated. It is perfectly `feasible, forexample, to adjustably'connect the driving rod to the vibratory elementof the driving device, to bodily move either the valve-chest and horn orthe driving device parallel to the base-plate 17 or to provide thenecessary relative movement of the various elements in any otherconvenient manner.

The driving devices, also, may be of any desired type capable oftranslating fluctuating electric currents into physical movements of therod 1l extending to the valve-head, or the rod may be immediately ormediately connected to the styluscarrying arm of a phonograph (notshown). I have, accordingly, illustrated the driving device merely as arectangle devoid of specific details. The adjustment of the driver withreference to the valve, once established for a given input air pressuremay be kept constant by a bracket or lock 26 whereby also microphoniceffect and external audio feed-back is suppressed.

It is important, however, to so proportion the moving element of thedriving device and the valve-head that the system is naturally resonantyto a frequency toward the upper limit of the acoustic frequencies to bereproduced. When this is done, the system is stiffness controlled andthe valve amplitude, at all frequencies below the natural period of thesystem, is substantially constant. Specifically, stiffness control isobtained by using a light valve-head in the valve and large restoringforce in the vibratory system. The initial valve-head lift at a giveninput air pressure is controlled for optimum operation by a mechanicaland a pneumatic adjustment which will be indicated later.

Although my invention is not'to be limited by any present theory ofoperation or principle, it would seem that the remarkable resultsobtained thereby in sound reproduction may, in part at least, beattributed to the fact that it provides pneumatic means for biasing anair current in somewhat analogous manner as the space-current in athermionic tube is biased by a C-potential applied to the grid thereof.In other words, I cause the main air current to be divided into aplurality of thin sheets which, by reason of the construction of thevalve-chest, are caused to reverse their direction of flow in a commonthrottling chamber to build up a bias pressure therein, and then toexpand, exponentially, into a common conduit which, in turn, expandsexponentially to free air. The bias pressure is controlled by anadjustable pneumatic leak connected to atmosphere. The air passages,between the throttling area and free air, are devoid of abrupt changesin continuity which would tend to cause reflections and distortion.

It lies within the scope of my invention to provide any suitable meansfor dividing an air current into thin filaments or sheets and forrecombining the filaments or sheets into a common exponential conduitsubsequent to the throttling operation. I have, however, found it veryconvenient to construct the valve-seat from a plurality of peculiarlyshaped predominately flat lamin 27, 29, 31, and 33 which, when sweatedtogether or otherwise held in correct relative position, define aplurality of air channels that reverse their direction in a commonthrottling chamber 35 one side of which is constituted by the valve-head7.

The preferred shapes of the lamin, and the directions of flow of the aircurrents in the passages dened thereby, from an inlet port 37 to thecommon outlet conduit, will be self-evident upon an-inspectionof Fig. 3of the drawings. The lamin 33, it will be noted, are stream lined towardthe common outlet conduit, or horn, for the purpose of reducing hiss andto permit each air-sheet to expand, exponentially, before it merges withthe remaining sheets.

By making the laminae` flat the assembly of the device is facilitated.They may, however, be cylindrical or otherwise curved, without departingfrom the spirit of my invention.

In order that the valve-head 7 shall be satisfactorily balanced inoperation, T have found it expedient to provide means for that purposesomewhat analogous tothe grid-leak resistor and biasing batterylutilized in connection with the use of a thermiomc tube as a detector.Such means, preferably, takes the form of an outlet conduit 39 extendingto free air from the valvechest, through which, under control of anadjustable valve 4l, air is permitted to leak to an extent suliicient tomaintain the average pressure behind the valve-head slightly less thanthe average pressure on the face thereof. It is, of course, feasible toderive the biasing pressure directly from the main air supply, through aseparate reducing valve, if necessary. Such modification being more orless obvious, it has not been illustrated.

A conduit 43, communicating with the inlet port 37, permits the inletair pressure to be observed and a reducing valve (not shown) may beinterposed between the inlet port and the source of air supply forassuring the correct operating pressure.

To prevent the valve-head from self-oscillation, it is advisable toprovide adjustable damping means therefor. The damping means may takethe form of a layer 45 of sponge rubber or other material having thedesired properties, which is pressed against the rear face of thevalve-plate by an adjustable retaining plate 47. The retaining plate ispressed against the rubber layer by the inner end of a cylindricalelement 49 which threadedly engages an opening in the end 51 of thevalve-chest and which is provided with a knurled knob 53 through whichextends the valve-actuated rod 11. y

The valve-head clearance, with respect to the valve-seat, is primarilyadjusted by the screw 53 and by the bleeder-valve screw 41. In general,the valve clearance is a function of (l) the magnitude of the input airpressure, controlled by a reduction valve (not shown), (2) thebias-pressure which builds up in the valvechamber, controlled by thebleeder-valve, (3) the pressure exerted by the damping means, controlledby the screw 53, and (4) the armature adjustment, controlled by thescrew 25.

The combination of the adjusting means enumerated provides for optimumoperation over a wide range of air pressures. In fact, my improved airflow speaker is so extremely flexible that substantially perfect resultshave been obtained with pressures varying from zero to sixty pounds persquare inch and h'igher.

The function of the adjustment means is easily understood by consideringthe operation of each separately, keeping in mind that the stiffness ofthe vibratory system is largely due to the compressed damping layer ofspon'ge rubber which covers the valve-head.

` When the input air pressure is off, the valvehead rests on the seatand the armature of the. driving mechanism is out of center, Byadmitting the input air pressure to the valve chest the valve-head islifted automatically from its seat, establishing an initial valveclearance of the order of 1.5 mils at approximately 40 pounds per squareinch input pressure and the armature of the driving mechanism must bethen in the central position.

The voice-current causes deflection of the valve-head which at maximumvolume are of a magnitude of less than 1.5 mils in my present samples.

In the operation of my improved air-flow speaker, air at a pressureoffrom zero to sixty pounds per square inch is supplied to an inlet port37. This input pressure should be maintained reasonably constant,preferably by suitable means adjacent to said inlet port.

As indicated by the arrows in Figs. 2 and 3, the incoming air currentdivides into a plurality of thin sheets which flow into the valve cham-Y ber, reverse their direction in the said chamber and now outwardly tothe horn. The face of the valve-head is, broadly speaking, the locus ofreversal of flow of all the currents. The average clearance between thevalve-head and the valveseat, being slightly more than one mil, isconsiderably less than the thickness of one of the air-sheets and theair, consequently, has greater velocity in the valve chamber than itdoes in the passage-ways defined by the lamin of the Self-oscillation,however, is primarily suppressed by the damping layer 45 which ispressed against the entire back surface of the valve-head by theadjusting screw 53 and retaining disk 47. It is also feasible tosuppress self-oscillations by feeding into the valve chamber, rearwardlyof the valve-head, air pulsations derived from any sultable source suchas the input conduit, Incidentally, those self-oscillations are of sucha forceful, almost destructive character that they suggest the use ofthe device as a powerful and efficient fog-horn.

When the valve-head is caused to vibrate the air-flow in thevalve-chamber is throttled in proportion to the movement of the platebut it is never completely stopped.l The throttling action requiresonlyva small expenditure of power since the valve is partially balancedby the back-pressure thereon determined by the bleeder valve 41 andsince the air current through the valve chamber has very high velocity.As a consequence, my improved loudspeaker is capable of giving enormousvolume without distortion, the amount of acoustic watts radiated beingmany times the amount of electric watts required to operate the drivingmechanism.

Among the principal advantages of my irnproved valve mechanism may beenumerated the following:

a. It requires no transverse adjustment. The well-known Parsons valverequires a very careful transverse adjustment in order that therectangular bars of its grill-shape valve-head and the slits of thevalve-seat shall be aligned. The slits in such a valve are over--lappedby the bars for a distance of only a few mils, thus making the effectivethrottling area of the valve small, when it is properly adjusted, ascompared with the utilization of possibly two-thirds or more of thevalve-seat area in my improved device.

b. By virtue of its relatively long throttle paths, the throttlingaction of my improved valve is mainly due to viscous air-flow resistancein contradistinction to the predominantly turbulent air-ow resistancewhich is set up in the Parsons valve. The modulation of air-flow by thevariation of a viscous resistance produces a better tone quality thanthat obtained by variation of a turbulent resistance because, in thelatter case, the tendency toward non-linear distortion and toward areduction of the percent modulation at larger initial valve clearancesis greater.

c. For similar reasons the load carrying capacity of my improved valveis larger.

d. By properly adjusting the clearance in my improved valve, the initialleakage and hiss may be made considerably smaller than in valves havingpredominant turbulent resistance modulation. And, moreover, the airconsumption will be comparatively small.

e. The valve-head is rigid in construction. Valves of the type having avibratory grill, as heretofore constructed, are rather delicate andeasily damaged. My improved valve-head, however, being in the form of arectangular or circular plate of aluminum or other light material, issubstantially immune to damage during use.

f. The valve-head surface and the valve-seat may be modified as tocontour to give any desired type of response. In other words. thevalve-head may be provided with a plurality of rectilinear or circularchannels of any desired contour and the ends of the lamina; between theinlet and outlet openings in the valve-head may be shaped to correspondto the channels. Furthermore, if desirable, the valve-head face adiacentvalve seat 5 may be of any suitable material to obviate the chatterintroduced by occasional over-loading, a feature which is substantiallyimpossible of introduction into valves of customary type.

g. The valve mechanism is relatively inexpensive. It may be built upfrom sheet metal punchings soldered or brazed together and the size ofthe air channels is limited only by the thickness of the punchings. Thisfeature is considered by me to be a radical improvement over valves ofthe customary type, since it enables more effective throttling withoutweakening the valve-seat structure.

h. The provision of balancing or biasing means of the valve. If thevalve of my improved airow loudspeaker were operated in the open, i. e.with atmospheric pressure acting only on the rear face of thevalve-head, the pressure of the air supply would cause the valve-head tobe driven away from the seat. By introducing an adjustable pressure dropbetween the high pressure side of the valve-head and the rear facethereof, the resultant force tending to drive the valve-head away fromthe seat may be so adjusted that the valve-head is held in the positionwhere the speaker operation is the best.

i. The provision of the valve bias chamber permits establishing acousticcounter-feed-back means to neutralize self-oscillation.

j. Prevention of reed-effect. The provision of controllable dampingmeans covering the valvehead prevents the said valve-head fromself-oscillation. This provision is impossible in the customary valves.The phenomenon of self-oscillation is often noticed in air-flowloudspeakers and is the cause of undesirable distortion and howling.

k. Maximum acoustic radiation efficiency may be obtained because it iseasy to provide or construct a conduit of exponentially increasingcrosssection from the throttling area to the mouth of the horn. This issubstantially impossible to obtain with valves of other types with whichI am familiar.

Z. The valve can be operated at higher air pressures than customary andis, accordingly, self-cleaning.

Although I have illustrated and described a specific embodiment of myinvention, numerous modifications thereof will be apparent to thoseskilled in the art to which it pertains. My invention, therefore, is notto be limited except insofar as is necessitated by the prior art and bythe spirit of the aprendedeclaims.

I claim as my invention:

1. The method of sound production which includes providing a pluralityof separate air currents, causing said separate currents to flow insubstantially the same direction in parallel paths, then causing thecurrents to combine and change their direction of flow, and throttlingthe combined currents at the locus of direction-change withoutcompletely stopping the flow thereof.

2. The method of sound production which includes providing a pluralityof air currents, causing said currents to flow in substantially the samedirection, then causing the currents to reverse their direction of flow,throttling the currents at the loci of their reversal and thereaftercombining the currents.

3. The method as set forth in claim 1 characterized in that the changein direction of the air current is substantially 180 degrees.

4. The method of sound production which includes providing a pluralityof air currents, causing the currents to reverse their direction offlow, constraining said air .currents to flow in thin sheets immediatelybefore and subsequent to their reversal, throttling the currents at theloci of their reversal, and thereafter combining the currents.

5. The method of sound production which includes providing a pluralityof air currents, causing the currents to reverse their direction offlow, throttling the currents at the loci of their reversal, thereaftercombining the currents, and then permitting the combined air currents toexpand exponentially into free air.

6. A sound-producing device comprising means providing a passageway foran air current and means for causing the current to substantiallyreverse its direction of flow between entering and leaving'saidpassageway, said last named means serving also to throttle the currentin accordance with the sound it is desired to produce.

7. The invention as set forth in claim 6 further characterized in thatmeans are provided for adjusting the operative position of thethrottling means.

8. The invention as set forth in claim 6 further characterized in thatmeans are provided for pneumatically adjusting the operative position ofthe throttling means.

9. The invention as set forth in claim 6 further characterized in thatdamping means are provided for the throttling means.

10. A sound producing device including a movable valve, a valve seathaving a plurality of openings therethrough, inlet means communicatingwith certain of said openings and outlet means communicating with theremainder of said openings.

l1. The invention as set forth in claim 10 characterized in that thevalve and valve-seat are substantially planar.

12. The invention as set forth in claim 10 further characterized in thatthe inlet openings through the valve-seat are adjacent to the outletopenings therethrough.

13. A sound producing device comprising means providing a plurality ofinlet passageways for air currents, a valve-chamber communicating withsaid passageways, means providing a plurality of outlet passageways fromthe valve-chamber, and a movable valve-head disposed in said chamber andadapted to throttle air-currents in their passage through the saidchamber.

14. The invention as set forth in claim 13 further characterized in thatthe outlet passageways increase in area smoothly.

15. 'Ihe invention as set forth in claim 13 wherein the outletpassageways increase in area smoothly, and further characterized in thata common outlet leading to free air is provided into which saidpassageways merge.

16. The invention as setforth in claim 13 further characterized in thatthe outlet passageways merge smoothly into a common outlet leading tofree air.

17. An air-flow loudspeaker including a valveseat, a valve-headcooperating therewith, said valve head being of relatively light weight,and a vibratory system associated with said valve for providing arelatively large restoring force thereto whereby the valve head isstiffness controlled".

18. An air-flow loudspeaker including a valveseat, and a stiffnesscontrolled valve head cooperating therewith, the natural period of themoving elements of said loudspeaker including the valve head being ofthe order of from 2500 to 5000 cycles per second.

19. In combination, a valve-seat in which terminate a plurality ofparallel inlet and outlet channels and a valve-head movably supported inproximity to said seat to define, with the valveseat, a commonthrottling chamber communicating with said channels.

20. The method of sound production which includes providing a pluralityof separate air currents, causing said currents to combine and changetheir direction of flow, throttling the combined currents at the locusof direction-change without completely ,stopping the iiow thereof andthen causing said currents to again change direction and to ow inseparate paths.

21. A sound producing device including in combination, means providing avalve seat and a plurality of passageways terminating in said valveseat, a movable valve arranged in cooperative relation to said Valveseat to provide a passage- Way common to said iirst named passagewaysland means for imparting a stiffness control thereto, including acompressed layer of damping material associated with the valve.

22. A sound producing device including in combination, an inlet port,conduit means for dividing an air current therefrom into thin lamentaryair currents, a valve seat and a valve cooperating therewith to providea passageway for simultaneously receiving, combining and reversing thedirection of flow of said filamentary air currents, conduit meanscommunicating with said passageway for again dividing said air currentinto thin lamentary air currents, and a common conduit into which saidlast named conduit means are arranged to discharge.

23. A sound producing device including a movable valve, a valve seathaving a surface and a plurality of substantially parallel passagesterminating in openings in said surface, inlet means communicating withcertain of said passages and outlet means communicating with theremainder of said passages.

24. A sound producing device including a movable valve, a valve seathaving a plurality of openings therethrough, inlet means communicatingwith certain of said openings and outlet means communicating with theremainder of said openings, the moving elements of said device includingthe valve having a natural resonance period toward the upper limit ofthe acoustic frequency range of sounds to be reproduced.

25. A sound producing device including in combination, means providing avalve seat and a plurality of passageways terminating in said valveseat, a movable valve arranged in cooperative relation to said valveseat to provide a passageway common to said first named passageways andmeans for imparting a stiffness control thereto, including a compressedlayer of damping material associated with the valve, the moving elementsof said device including the valve having a natural resonance periodtoward the upper limit of the acoustic frequency range of sounds to bereproduced.

JURJEN S. HIGH.

